To obtain hydrocarbons such as oil and gas, wells (also referred to as “wellbores” or “boreholes”) are drilled by rotating a drill bit attached at a drill string end. A large number of the current drilling activity involves directional drilling, i.e., drilling deviated and horizontal boreholes, to obtain increased hydrocarbon production from subsurface formations. Such wellbores are often drilled along complex well paths. The systems used to drill such wellbores generally employ a drill string that has a drilling assembly (also referred to as a “bottomhole assembly” (BHA)) and a drill bit at an end thereof. The drill bit is rotated by rotating the drill string from the surface and/or by rotating the drill bit by a drilling motor (also referred to as the “mud motor”) disposed in the drilling assembly. A drilling fluid (commonly known as the “mud” or “drilling mud”) is pumped into a tubing of the drill string to rotate the drilling motor and the tubing is rotated by a prime mover at the surface, such as a motor. The drill bit is typically coupled to a bearing assembly having a drive shaft which in turn rotates the drill bit attached thereto. Radial and axial bearings in the bearing assembly provide support to the radial and axial forces of the drill bit.
A number of devices and sensors carried by the BHA measure various parameters or characteristics associated with the drill string. Such devices typically include sensors for measuring pressure, temperature, azimuth, inclination, vibration, etc. The BHA also includes a variety of other devices or sensors, such as resistivity, acoustic, nuclear, nuclear magnetic resonance sensors, etc., which devices are commonly referred to a “measurement-while-drilling” (“MWD”) or logging-while-drilling (“LWD”) tools or sensors. MWD sensors are used to determine properties of the earth formation and the extent of the hydrocarbons contained in the formation. These devices and sensors contain complex and sensitive sensors and electronic components, which may remain disposed in the wellbore for several hours to days.
The BHA, during drilling of a wellbore, is subjected to varying load conditions, which may be due to bending moments exerted on various elements of the BHA by side forces acting on the BHA, vibration, weight on bit, etc. These forces can be caused by gravity, drilling dynamic effects and/or by contact between the wellbore wall and the BHA. The bending moments can cause deviations from the desired wellbore path. It is therefore desirable to measure loads on one or more components of the BHA and the movement or displacement of certain elements of the BHA with respect to fixed points or relative to other members so that actions may be taken to maintain the BHA within certain operating limits during drilling of the wellbore.
The disclosure herein provides apparatus and method for estimating loads and other parameters of interest relating to a wellbore operation.